Apparatuses using plasma, such as a dry etching apparatus, a CVD apparatus, a PVD apparatus, and the like, use not only radio-frequency waves for plasma generation, but also bias frequencies for controlling the generated plasma by giving energy thereto (radio-frequency waves for plasma control). In current techniques, a plurality of bias frequencies are superimposed and applied to an electrostatic chuck, thereby individually controlling multiple flux energies of ions or electrons in the plasma state.
As a technique related to such a conventional art, there is known a device and a method in which an etching process target attracted to an electrostatic chuck to which a DC voltage is applied between at least paired flat electrodes embedded in an insulating layer is etched in a plasma generated by application of a radio-frequency voltage (Japanese Patent No. 2,651,597). As another technique, there is known a double-electrode wafer holder in which the radial profile of a plasma density on a wafer is improved (Japanese Laid-open Patent Publication No. 2003-133398).
In a dry etching apparatus or the like using plasma, when radio-frequency waves are fed simultaneously to portions having an electrical potential relative to ground, the density of in-plane ion energy generated by the application of the radio-frequency waves is automatically determined by such an influence as the skin effect corresponding to the radio-frequency waves applied or by the configuration of the electrostatic chuck. When the in-plane (e.g., a center portion and a periphery portion of a wafer) control is performed individually as independent distribution control (IDC) does, a frequency and an output need to be selected appropriately. However, such selection is quite difficult, making the in-plane distribution control also difficult.
For example, as is exemplified in FIG. 1A to be described later, in a mode where radio-frequencies for plasma control (RF1, RF2) are simultaneously applied to a base plate 1, the in-plate density distribution (i.e., the density distribution of ion energy on the wafer for performing a process such as etching) is determined by the skin effect corresponding to the frequency applied or the shape of the base plate 1. For this reason, there is a problem that efficient, flexible control of the density distribution is difficult to achieve. The ion energy density in an outer periphery portion of the wafer particularly varies widely, resulting in variations in how the wafer is processed through etching or the like, compared to other portions.
In addition, since the radio-frequency (RF1, RF2) powers fed to the base plate 1 control the plasma by being propagated through an electrostatic chuck substrate 3, the thicker the substrate 3, the more power loss occurs. Accordingly, radio-frequency powers more than required for plasma control has to be fed to the base plate 1.
On the other hand, another problem arises if the thickness of the electrostatic chuck substrate 3 is reduced to make the power loss small. Specifically, when the electrostatic chuck substrate 3 is made thin, an adhesive layer 5 fixedly holding the electrostatic chuck substrate 3 to the base plate 1 is to be located in a relatively upper portion of the electrostatic chuck, which makes the adhesive layer 5 more likely to be exposed to plasma or gas.
Since a material constituting the adhesive layer 5 is less durable to the plasma and the like than that of the electrostatic chuck substrate 3 and is easily damaged, the adhesive layer 5 is therefore easily deteriorated. Accordingly, when the adhesive layer 5 deteriorates, insulation and adhesion effects between the electrostatic chuck substrate 3 and the base plate 1 are lost. As a result, there is a problem of a reduction in the overall life of the electrostatic chuck.
As exemplified in FIG. 1B to be described later, such a problem may occur similarly in a mode in which not only a DC voltage for attraction but also radio-frequency waves (RF1, RF2) for plasma control are applied simultaneously to an electrostatic-attraction electrode layer 4a. 